It is known to provide touch screens in vehicles to allow the driver or passenger to control various sub-systems of the vehicle. It is also known to provide proximity sensing systems in which a signal is transmitted through the driver or passenger, for example between an antenna in their seat and a control input such as a push button or touch screen, and the strength of the received signal measured. The strength of the signal indicates the capacitance between the driver or passenger and the control input, and therefore the distance of the user's hand from the control input. Typically the signal is received at, or transmitted from the control input by means of a specially provided antenna, such as a conductive coating on the push button, or a conductive bezel around the touch screen.
According to the invention, there is provided a touch screen control system comprising a touch screen having first and second conductive layers arranged to be brought together by touching of the screen, and a detection system arranged to detect a contact position at which the screen is touched by monitoring electrical signals from at least one of the layers, wherein the system further comprises an antenna, and the detection system includes a proximity sensing signal generator arranged to generate a proximity sensing signal to be transmitted between the antenna and the first layer via a user of the system, and the detection system is further arranged to receive the transmitted proximity sensing signal and determine therefrom the distance between a part of the user and the touch screen.
The first layer may have two contact elements extending along opposite sides thereof, and the detection system may be arranged to connect the contact elements to different potentials so that the potential of the layer varies with the distance from each of the two contact elements thereby to enable sensing of the contact position. Such an arrangement is consistent with a convenient four-wire touch screen design.
The detection system may be arranged to transmit the proximity sensing signal from the first layer to the antenna, or from the antenna to the first layer. The detection system may be arranged to transmit, or receive, the proximity sensing signal via at least one of the contact elements, and preferably both of the contact elements.
Where the proximity sensing signal is transmitted to the first layer, the detection system preferably includes a summing device arranged to sum signals from the two contact elements to produce a received proximity sensing signal.
The detection system may be arranged to control at least one connection to the second layer such that it acts as a shield for at least part of the time when the proximity sensing signal is being received. For example, the detection system may be arranged to determine when the touch screen is being touched, and to control said at least one connection to connect the second layer to at least one fixed potential when the proximity sensing signal is being received and the touch screen is not being touched.
Conveniently, said at least one connection may comprise the normal connections to the second layer used for touch position sensing. For example they may comprise two connections arranged to connect the second layer between two different potentials, both when the proximity sensing signal is being received and the touch screen is not being touched, and when the detection system is determining the contact position.
The detection system may be arranged to electrically isolate the second layer when the proximity sensing signal is being received and the touch screen is being touched. This avoids potentials on the second layer interfering with the proximity sensing signal received on the first layer.
The detection system may be arranged to alternate between a touch position sensing mode, in which it is arranged to determine the contact position, and a proximity sensing mode, in which it is arranged to measure said distance.
The detection system may comprise a touch screen controller arranged to detect the contact position, and a proximity sensing system including the proximity sensing signal generator. The touch screen controller may then be arranged to receive said electrical signals, including the proximity sensing signal from the touch screen and the proximity sensing system may be arranged to receive the proximity sensing signal from the touch screen controller. The touch screen controller may also be arranged to send a synchronisation signal to the proximity sensing system to enable the proximity sensing system to determine when it is receiving the proximity sensing signal from the touch screen controller.
The present invention further provides a touch screen control system comprising a touch screen having first and second conductive layers arranged to be brought together by touching of the screen, and a detection system arranged to detect a contact position at which the screen is touched by monitoring electrical signals from at least one of the layers, wherein the first layer is arranged to act as a receiving antenna to receive a proximity sensing signal transmitted from a transmitting antenna via a user, and the detection system is further arranged to transmit the received proximity sensing signal on to a proximity sensing system thereby to enable the proximity sensing system to determine a distance between a part of the user and the touch screen.